Approximately 400,000 deaths in the United States each year are attributable to poor diet and physical inactivity. Despite the well-documented health benefits of regular physical activity and diets high in fruits and vegetables and low in fat, the prevalence of these behaviors remains relatively low in the population as a whole, and even lower in minority and socioeconomically disadvantaged subgroups. The overall purpose of this proposal is to evaluate the efficacy of a cost-effective, 4-month computerized diet and physical activity intervention program, delivered by e-mail, within the worksite environment. The intervention program will be built on an existing prototype that showed both technical feasibility and potential scientific merit in a 12-week pilot study. In the first stage of the current study, we will develop that prototype further both in terms of content and technical capabilities. Specifically, we will add a physical activity component (designed to increase walking and decrease sedentary behavior), and will further tailor messages to participants' stage of readiness for change, self efficacy and lifestyle characteristics. We will also enhance the interactive features, such as a tool that simulates the overall effects of a specific change in diet or physical activity. In the second stage of the study, we will conduct a 2-arm randomized trial of the intervention program in employees of Northern California Kaiser Permanente (KP). Approximately 2,000 employees from 20 regional KP departments will be invited to participate in the trial through an e-mail from KP leaadership that describes the study, followed by an e-mail from the study staff containing baseline assessments, instructions, and informed consent. Employees who are interested in participating will return the forms by e-mail directly to study staff. Employees will be randomly assigned, in roughly equal numbers, with the department as the unit of randomization, to the intervention group, who will receive the full intervention program, or the wait-list control group, who will receive standard diet and physical activity recommendations and information. The control group may choose to receive the intervention at the end of the study period. To determine both shortterm effects and longer-term sustainability of effects, both groups will complete dietary and physical activity assessments and other questionnaires (self efficacy, social support, health-related quality of life, and demographic characteristics) at the beginning of the trial, after the 4-month intervention, and then again 8 months from baseline. In addition to physical activity and dietary behaviors, study outcomes will include health-related quality of life, absenteeism, and health care utilization. Primary analyses of differences between the intervention and control groups will be based on "intent to treat," and will account for the cluster randomization design. This e-mail-based intervention, if proven successful, could be widely and cost-effectively disseminated and, thereby contribute significantly to achieving the dietary and physical activity goals for Healthy People 2010.